Usually, in the thrust-reversal position, a thrust reverser obstructs at least part of the gas ejection stream in the aft direction, re-directing it towards the sides, or better towards the front of the turbojet, thereby generating reverse thrust that assists the braking provided by the wheels of the airplane. At very least, the thrust reverser reduces the speed of the gas jet stream in the aft direction from the turbojet.
The means implemented to perform this re-direction or at least this reduction in speed of the outgoing stream in the aft direction vary depending on the type of reverser. As a general rule, the architecture of a reverser comprises deflector means that are movable between firstly an open or thrust-reversal position in which the reverser operates and reduces the speed of the outgoing stream in the aft direction, and secondly a retracted or closed or normal position in which the turbojet performs its normal propulsion function.
Two different types of reverser are known.
In reversers using doors, the doors obstruct the secondary stream and divert it towards the front of the airplane.
In a cascade type reverser, sliding doors open the nacelle while also pulling flaps that obstruct the secondary stream.
In another known embodiment, the thrust reverser is formed by an aft portion of the nacelle that is constituted by a moving portion that can move up in order to put itself in a position for reversing thrust and deflecting the secondary stream, or it can return forwards so as to become once more an integral portion of the nacelle, then enabling the turbojet to operate normally (see patent EP 1 416 147).
Those various provisions make use of mechanical structures that are relatively complex and that are generally carried by the nacelle of the turbojet. Such complexity means that the reverser presents significant weight and overall is excessively expensive, given the short length of time (a few seconds) for which it is used compared with the duration of a flight. Furthermore, since the nacelle of a turbojet is the largest-diameter portion thereof, the reverser is necessarily of large dimensions, and consequently features as one of the predominant and highly penalizing elements in the weight budget of the thruster assembly. Its fabrication cost and its utilization cost (associated with its weight) are thus high. Its presence also prevents the size of the nacelle being reduced; the reverser prevents a more aerodynamic nacelle profile being adapted, i.e. it prevents the maximum diameter of the nacelle being reduced, even though that would enable the performance of the turbojet to be improved.